Recently, a vehicle-mounted driving recorder has been developed that can automatically record an image of outside or inside of a motor vehicle (an automobile) during driving and that can make an after-the-fact analysis on an objective situation at a time of an accident or hiyari-hatto, and there is a trend that this kind of a driving recorder is mounted on, for example, a taxicab in order to prevent an accident by making the after-the-fact analysis on an ordinary driving or to investigate an objective evidence of a cause of the accident when the accident occurs.
Concretely, the driving recorder of this type is mounted on a vehicle, and so arranged to sequentially and chronologically store situation data such as outside image data, acceleration data, speed data and position data while the vehicle is driving in a memory so that an after-the-fact analysis can be made by reference to the situation data stored in the memory.
It is often difficult to store all of the situation data during driving due to the capacity of the memory, although it depends on duration of driving. When a capacity of the memory runs out, it stops to write the situation data, resulting in failure of recording the latest situation data.
Then, conventionally known are an arrangement of, so-called a ring-buffer memory method, wherein the oldest situation data is updated in sequence when the capacity of the memory runs out, and an arrangement wherein, a hiyari-hatto, an accident or an abnormality is considered to occur at a time when acceleration (deceleration) of the vehicle shows above a certain numerical value, the situation data alone during a certain period before and after the time of the event is recorded in a nonvolatile memory to use the situation data for after-the-fact analysis from a temporary memory (refer to the patent document 1).
With the ring-buffer memory method, however, there is a case that necessary situation data is buried in the updated data and deleted. For example, in case of an accident, since there would be no chance that the vehicle continues to run any more, necessary situation data is considered to be included in the latest situation data so that it would not be a big problem. In case of a hiyari-hatto, however, necessary situation data to prevent the accident might be buried in the old situation data and deleted. As a result, the ring-buffer memory method is not preferable.
In addition, with the method of judging by the use of the acceleration, since a lot of unnecessary situation data in case of other than an accident or hiyari-hatto (in case of just opening or closing a door, or quick acceleration or deceleration due to a driver's driving preference) is obtained, a capacity of a memory runs out in a short time and it becomes very troublesome to select unnecessary situation data after the event.
A driving recorder that selects and stores only the situation data whose importance is high in a recording media generally uses acceleration data as a trigger for detection and the situation data before and after a time when the acceleration is detected in case the acceleration is bigger than a certain level is stored in the recording media (Patent document 1).
If situation data is selected by the use of the acceleration data as a trigger for detection, however, the situation data is likely to be selected and stored at a time when the trigger for detection reacts to the acceleration generated just due to a bump on a road, a movement of opening or closing the door or pressing a brake pedal. In this case, there is a problem that it becomes difficult to analyze the situation data after the event because the situation data whose importance is low is also recorded and stored massively and there is also a problem that it becomes impossible to store the situation data whose importance is high because a recording media is filled with the situation data whose importance is low.    Patent document 1: Japan patent laid open number 5-197858